I really don't sees it as a bad practice withdrawing some profit from your Bitcoin investment, if you have gotten to that over accumulation status, where the problem lies is selling everything off and becomes a no coiner all of a sudden, that's where the problem lies if you ask me, because at some point, we have to enjoy the fruit of our labour.
What I find problematic is the stipulated timeframe you intend holding, holding just for two circles doesn't seems like long to me because if you can attain that height of over accumulation status during that timeframe, you need to hold for one or two more circle for your Bitcoin investment to give you the best possible result you envision before starting, so in essence of what am trying to say is that 8 years is too small to be term as long term.
There's absolutely nothing wrong with withdrawing some profits out of your bitcoin investment. Nothing is wrong with it besides we're humans and not robots and we have our needs and emergencies sometimes which supersedes our investment plans.
If you have reached your accumulation goals and perhaps you feel you have done enough buying and holding over the years and probably you have reached a point in life where you no longer work actively to earn from other means, then you can begin to think about taking out so of your bitcoin to sort out your needs after all there is a saying that "the money you save today will save you tomorrow". However, you must be careful not to justify reckless withdrawal of your bitcoin else you will run out of bitcoin in the near future. JJG made a very interesting thread
JJG's Bitcoin Investment Ideas (Sustainable Withdrawal / Portfolio Maintenance) to help with minor details that will make the withdrawal process and not harm your portfolio.